With the advance in recent years of microminiaturization in the manufacture of semiconductor devices and semiconductor chip mounting boards, there have beer increasing demands for higher resolving power in the exposure apparatus used to manufacture these items. To satisfy this demand, the wavelength of the light source of the apparatus must be shortened and/or the NA (numerical aperture) of the projection optical system of the apparatus must be increased. If the wavelength is shortened, the optical glasses that can withstand practical use is limited due to the absorption of light. Furthermore, when it comes to the short wavelengths of ultraviolet rays and X-rays, usable optical glasses are nonexistent. In this case, it is impossible to construct reduction projection optical systems that are dioptric or catadioptric.
A reduction catoptric projection optical system is disclosed in, for example, U.S. Pat. No. 5,815,310. The projection optical system disclosed therein includes two sets of reduction optical systems comprising reflective surfaces with a concave-convex-concave configuration, and forms an intermediate image between the two reduction optical systems. This projection optical system has the advantage that its six reflective surfaces increase the number of degrees of freedom for aberration correction. Further, a plane reflective mirror is not needed just for the return path, since the number of reflective surfaces is naturally even. In addition, since the reduction magnification of the entire optical system can be distributed among the reduction optical systems, it has the advantage that the burden of each reduction optical system can be lightened. Unfortunately, however, because the two reduction optical systems are joined by a pair of mirror pairs, the diameter of the mirror pairs unavoidably increases. This results in increased cost of the projection optical system.